There is disclosed in U.S. Pat. No. 3,752,097 issued Aug. 14, 1973, in the names of George A. Fuller, Jr. et al improved mechanism for performing automatically the edge finishing of workpieces, notably those of flexible fabric having peripheries including both straight and curved portions. According to the invention therein set forth an over-edging machine of known type, for instance, is provided with an automatic corner turning mechanism whereby a swing finger and cooperative rotary clamp are operative in response to an external work edge sensor to enable the over-edging machine to progress rapidly over a margin of a rectilinear path, about a convex "corner", and thence along another straight line path. The guidance sensor controls movement of the swing finger and clamp in response to the position of successive peripheral operating points solely along the external margin of the work.
The indicated guidance control has been found to be commercially satisfactory in dealing with such items as most face cloths, small towels, and the like. Some workpieces, however, require a different mode of automatic guidance in determining their ultimate peripheral configuration. One example is conveniently afforded by face cloths and the like which initially have a pile or terry spaced inwardly from a woven margin that is thinner and free of terry material, but which are to be produced wholly free of such margins. That is to say the edge processing such as overedging is to occur directly along the inner edge of terry material. In edge finishing such work it is desirable to automatically guide the work in a manner whereby the terry edge will be progressively relieved of the non-terry material and progressively bound as by overedging. This entails a need for guidance sensing in two modes, as herein shown, not from the initially external perimeter or raw outside edge of the work, but from discriminating the inner demarcation or inner contour provided by the limit of the upstanding loops of terry. At present guidance of flexible workpieces having margins distinctive from their interior is largely manual, relatively slow, and the results not entirely uniform, especially about the convex "corners" of a multisided periphery.